The present invention relates to a method for printing fibrous textile materials using the ink-jet printing technique.
Ink-jet printing processes have been used in the textile industry for some years. Such processes make it possible to dispense with the otherwise customary production of a printing screen, so that considerable savings can be made in terms of cost and time. Especially in the case of the production of pattern originals it is possible to respond to a change in requirements within a significantly shorter period of time.
Such ink-jet printing processes should especially have optimum characteristics from the standpoint of application technology. In this connection mention may be made of characteristics such as the viscosity, stability, surface-tension and conductivity of the inks used. Furthermore, higher demands are being made of the quality of the resulting prints, e.g. in respect of colour strength and fastness to wetting. Those demands are not met by the known processes in all characteristics, so that there is still a need for new processes for the ink-jet printing of textiles.
The present invention relates to a process for printing fibrous textile materials in accordance with the ink-jet printing technique wherein the fibrous materials are printed with an aqueous ink that comprises at least one acid dye and that has a viscosity of from 1 to 40 mPaxc2x7s.
Suitable acid dyes for the process according to the invention include, for example, the dyes described under xe2x80x9cAcid Dyesxe2x80x9d in the Colour Index, 3 rd edition (3rd revision 1987 inclusive Additions and Amendments up to No. 85). The anionic dyes that can be used may belong to a wide variety of dye classes and may contain one or more sulfonic acid groups. They include, for example, triphenylmethane dyes having at least two sulfonic acid groups, heavy-metal-free monoazo and disazo dyes each having one or more sulfonic acid groups, and heavy-metal-containing, namely copper-, chromium-, nickel- or cobalt-containing, monoazo, disazo, azomethine and formazan dyes, especially metallised dyes, that contain two molecules of azo dye, or one molecule of azo dye and one molecule of azomethine dye, bonded to a metal atom, especially such dyes containing mono- and/or dis-azo dyes and/or azomethine dyes as ligands and a chromium or cobalt ion as central atom, as well as anthraquinone dyes, especially 1-amino-4-arylaminoanthraquinone-2-sulfonic acids and 1,4-diarylamino- or 1-cycloalkylamino-4-arylaminoanthraquinonesulfonic acids.
There come into consideration as anionic acid dyes, for example:
a) triphenylmethane dyes of formula 
xe2x80x83wherein
R71, R72, R73 and R74 are each independently of the others C1-C4alkyl and R75 is C1-C4alkyl, C1-C4alkoxy or hydrogen;
b) monoazo and disazo dyes of formulae 
xe2x80x83wherein
R76 is benzoylamino, phenoxy, chlorophenoxy, dichlorophenoxy or methylphenoxy, R77 is hydrogen, benzoyl, phenyl, C1-C4alkyl, phenylsulfonyl or methylphenylsulfonyl, and the substituents R78 are each independently of the other hydrogen or a phenylamino or N-phenyl-N-methylaminosulfonyl; 
xe2x80x83wherein
the phenyl ring B10 may be substituted by halogen, C1-C4alkyl and sulfo and R79 is xcex1-bromoacryloylamino; 
xe2x80x83wherein
R76 has the meanings given above; and 
c) 1:2 metal complex dyes, such as the 1:2 chromium complex dyes of the azo and azomethine dyes of formulae 
xe2x80x83wherein
R80 is hydrogen, sulfo or phenylazo and R81 is hydrogen or nitro, and the phenyl ring B10 may be substituted by halogen, C1-C4alkyl and sulfo;
d) 1:2 metal complex dyes, such as the symmetric 1:2 chromium complex dyes of the azo dyes of formulae 
xe2x80x83wherein
the phenyl ring B10 may be substituted by halogen, C1-C4alkyl and sulfo and R82 and R83 are each independently of the other hydrogen, nitro, sulfo, halogen, C1-C4alkylsulfonyl, C1-C4alkylaminosulfonyl or xe2x80x94SO2NH2; and 
xe2x80x83wherein
R84 is hydrogen, C1-C4alkoxycarbonylamino, benzoylamino, C1-C4alkylsulfonylamino, phenyl-sulfonylamino, methylphenylsulfonylamino or halogen, R85 is hydrogen or halogen and R86 is C1-C4alkylsulfonyl, C1-C4alkylaminosulfonyl, phenylazo, sulfo or xe2x80x94SO2NH2, the hydroxy group in the benzo ring D10 being bound in the o-position relative to the azo group on the benzo ring D10;
symmetric 1:2 cobalt complexes of the azo dyes of formulae 
xe2x80x83wherein
R87 is an xe2x80x94OH or xe2x80x94NH2 group, R88 is hydrogen or C1-C4alkylaminosulfonyl and R89 is nitro or C1-C4alkoxy-C1-C4alkyleneaminosulfonyl, and 
asymmetric 1:2 chromium complex dyes of the azo dyes of formulae 
xe2x80x83wherein
one substituent R90 is hydrogen and the other is sulfo; 
xe2x80x83wherein
R81 is hydrogen or nitro, the phenyl rings B10 may be substituted by halogen, C1-C4alkyl and sulfo and R85 is hydrogen or halogen; and 
xe2x80x83wherein
the phenyl ring B10 may in each case be substituted by halogen, C1-C4alkyl and sulfo, R81 is hydrogen or nitro, R91 is hydrogen, methoxycarbonylamino or acetylamino and R86 is C1-C4alkylsulfonyl, C1-C4alkylaminosulfonyl, phenylazo, sulfo or xe2x80x94SO2NH2;
1:2 chromium complex dyes of the azo dyes of formulae (7) and (8);
1:2 chromium mixed complexes of the azo dyes of formulae (7) and (8); and
the copper complex of formula 
xe2x80x83wherein
the benzo rings D20 are substituted by sulfo or by sulfonamido;
e) anthraquinone dyes of formulae 
xe2x80x83wherein
R79 is xcex1-bromoacryloylamino, the substituents R92 are each independently of the others hydrogen or C1-C4alkyl and R93 is hydrogen or sulfo; 
xe2x80x83wherein
the substituents R94 are each independently of the other cyclohexyl or a diphenyl ether radical that may be substituted by sulfo and by the radical xe2x80x94CH2xe2x80x94NHxe2x80x94R79 in which R79 has the meanings given above; and 
xe2x80x83wherein
R79 is xcex1-bromoacryloylamino, R92 has the meanings given for formula (15) and R95 is C4-C8alkyl;
f) metal-free anionic anthraquinone dyes of formulae 
xe2x80x83wherein
(R96)1-5 denotes from 1 to 5 identical or different substituents selected from the group C1-C4alkyl unsubstituted or substituted by C2-C4alkanoylamino (which may in turn be substituted in the alkyl group by halogen) or by benzoylamino; C1-C4alkoxy; C2-C4alkanoylamino and C2-C4hydroxyalkylsulfamoyl; R97 is C1-C4alkyl, C5-C7cycloalkyl unsubstituted or substituted by C1-C4alkyl, or phenyl unsubstituted or substituted by phenoxy, C1-C4alkyl or by sulfo, the phenoxy group in turn being unsubstituted or substituted in the phenyl ring by C1-C4alkyl, C1-C4alkoxy, halogen or by sulfo, especially by C1-C4alkyl or by sulfo; R98 and R99 are each independently of the other C1-C4alkyl unsubstituted or substituted by C2-C4alkanoylamino (which may in turn be substituted in the alkyl group by halogen) or phenoxy unsubstituted or substituted in the phenyl ring by C1-C4alkyl, C1-C4alkoxy, halogen or by sulfo, especially by C1-C4alkyl or by sulfo; and
g) monoazo dyes of formulae 
xe2x80x83wherein
R100 is halogen, trifluoromethyl or 
xe2x80x83in which R103 is cyclohexyl and R104 is C1-C4alkyl, or the radicals R103 and R104, together with the nitrogen atom linking them, form an azepinyl ring; R101 is hydrogen or halogen and R102 is hydrogen or is phenoxy unsubstituted or substituted in the phenyl ring by halogen; 
xe2x80x83wherein
R105 is hydrogen, halogen or sulfo; R106 is hydrogen; halogen; phenoxy or phenoxysulfonyl unsubstituted or substituted in the phenyl ring by C1-C4alkyl, C1-C4alkoxy or by halogen; or a radical of formula 
xe2x80x83in which R110 is phenyl unsubstituted or substituted by C1-C4alkyl, C1-C4alkoxy, halogen or by sulfo, R111 is hydrogen or C1-C4alkyl and X50 is halogen; R107 is hydroxy or amino; and R108 and R109 are each independently of the other hydrogen or halogen; 
xe2x80x83wherein
R112 and R113 are each independently of the other hydrogen, C1-C4alkyl, C1-C4alkoxy, halogen or C2-C4alkanoylamino, preferably hydrogen or C1-C4alkyl, R114 is phenyl unsubstituted or substituted by C1-C4alkyl, C1-C4alkoxy, halogen or by C2-C4alkanoylamino, preferably unsubstituted phenyl or phenyl substituted by C1-C4alkyl; 
xe2x80x83wherein
R115 is hydrogen or C1-C4alkyl, R116 is hydrogen or phenylsulfonyl unsubstituted or substituted in the phenyl ring by C1-C4alkyl, C1-C4alkoxy, halogen or by C2-C4alkanoylamino, preferably unsubstituted phenylsulfonyl; 
xe2x80x83wherein
R117 is hydrogen, C1-C4alkyl, C1-C4alkoxy, halogen, or phenoxy unsubstituted or substituted in the phenyl ring by C1-C4alkyl, C1-C4alkoxy, sulfo, halogen or by C2-C4alkanoylamino, preferably unsubstituted phenoxy or phenoxy substituted by C1-C4alkyl or by halogen, and R118 is benzoyl unsubstituted or substituted in the phenyl ring by C1-C4alkyl, C1-C4alkoxy, sulfo or by halogen, preferably unsubstituted benzoyl, or C2-C4alkanoyl unsubstituted or substituted in the alkyl group by hydroxy or by C1-C4alkoxy, preferably unsubstituted C2-C4alkanoyl, e.g. acetyl; and 
xe2x80x83wherein
R119 is hydrogen, C1-C4alkyl, C1-C4alkoxy, halogen, or C2-C4alkanoylamino unsubstituted or substituted in the alkyl group by hydroxy, C1-C4alkoxy or by halogen; R120 is phenyl unsubstituted or substituted by C1-C4alkyl, C1-C4alkoxy, sulfo or by halogen, preferably unsubstituted phenyl, and
R121 is hydrogen or C1-C4alkyl;
and disazo dyes of formulae 
xe2x80x83wherein
A20 and A2, are radicals of formula 
xe2x80x83wherein
R107, R108 and R109, each independently of the others, has the meanings given above; 
There are preferred as anionic acid dyes the dyes of formulae (5), (8), (14), (18), (26), (27) and (28).
Suitable metal-free anionic acid dyes are, for example, C.I. Acid Yellow 79, 110 and 246; C.I. Acid Orange 67 and 94; C.I. Acid Red 127,131, 252 and 361; C.I. Acid Green 40:1 and C.I. Acid Blue 225, 239, 260, 277 and 324 and also, especially, the dyes of formulae 
In the acid dyes of formulae (1) to (26), the radicals R71 to R121 have the following meanings: alkyl groups having from 1 to 4 carbon atoms, such as methyl, ethyl, propyl, isopropyl and butyl, it being possible for the alkyl radicals to be further substituted, e.g. by hydroxyl, sulfo or by sulfato; alkoxy groups having from 1 to 4 carbon atoms, such as methoxy, ethoxy, propoxy, isopropoxy and butoxy, it being possible for the alkyl radicals to be further subtituted, e.g. by hydroxyl, sulfo or by sulfato; halogen, such as fluorine, bromine and, especially, chlorine; C1-C4alkylsulfonyl, such as methylsulfonyl and ethylsulfonyl; C1-C4alkylaminosulfonyl, such as methylaminosulfonyl and ethylaminosulfonyl; C1-C4alkoxycarbonylamino, such as methoxycarbonylamino and ethoxycarbonylamino; C1-C4alkoxy-C1-C4alkyleneaminosulfonyl, such as methoxyethyleneaminosulfonyl; C2-C4alkanoylamino, such as propionylamino; C2-C4hydroxyalkylsulfamoyl, such as xcex2-hydroxyethylsulfamoyl; C5-C7-cycloalkyl, such as cyclopentyl and cyclohexyl.
Of particular importance are the dyes of formulae (29), (30), (31), (45) and (59) to (64) and especially of formulae (29), (30), (31), (45), (59), (60) and (62) to (64).
The mentioned acid dyes are known or can be obtained analogously to known preparation procedures, such as disazotization, coupling, addition and condensation reactions.
The dyes used in the inks should preferably have a low salt content, that is to say they should have a total content of salts of less than 0.5% by weight, based on the weight of the dyes. Dyes that have relatively high salt contents as a result of their preparation and/or as a result of the subsequent addition of diluents can be desalted, e.g., by membrane separation procedures, such as ultrafiltration, reverse osmosis or dialysis.
The inks preferably have a total content of dyes of from 1 to 35% by weight, especially from 1 to 30% by weight and more especially from 1 to 20% by weight, based on the total weight of the ink. As a lower limit, a limit of 2.5% by weight, especially 5% by weight and more especially 7.5% by weight, is preferred.
Preferred for the process according to the invention are those inks having a viscosity of from 1 to 40 mPaxc2x7s (milliPascal-seconds), especially from 1 to 20 mPaxc2x7s and more especially from 1 to 10 mPaxc2x7s. Inks having a viscosity of from 1 to 6 mPaxc2x7s are of special importance. Also of importance are inks having a viscosity of from 10 to 30 mPaxc2x7s.
The inks may comprise thickeners of natural or synthetic origin, inter alia for the purpose of adjusting the viscosity.
Examples of thickeners that may be mentioned include commercially available alginate thickeners, starch ethers and locust bean flour ethers, especially sodium alginate on its own or in admixture with modified cellulose, especially in admixture with preferably from 20 to 25% by weight of carboxymethylcellulose. Synthetic thickeners that may be mentioned are, for example, those based on poly(meth)acrylic acids or poly(meth)acrylamides.
The inks comprise such thickeners, for example, in an amount of from 0.01 to 2% by weight, especially from 0.01 to 1% by weight and more especially from 0.01 to 0.5% by weight, based on the total weight of the ink.
The inks may also comprise buffer substances, e.g. borax, borates or citrates. Examples that may be mentioned include borax, sodium borate, sodium tetraborate, sodium hydrogen phosphate and also sodium citrate. They are used especially in amounts of from 0.1 to 3% by weight, especially from 0.1 to 1% by weight, based on the total weight of the ink, in order to establish a pH value of, for example, from 4 to 10, preferably from 5 to 8.
As further additives, the inks may comprise surfactants or humectants.
Suitable surfactants include commercially available anionic or non-ionic surfactants.
As humectants in the inks used in accordance with the invention there come into consideration, for example, urea, polyhydric alcohols, e.g. ethylene, diethylene, triethylene or tetraethylene glycol, 1,2-propylene glycol, dipropylene glycol, glycerol and polyethylene glycols having a molecular weight of preferably from 200 to 800, e.g. polyethylene glycol 200, and N-methyl-2-pyrrolidone.
If desired, the inks may also comprise acid donors, such as butyrolactone, or preservatives, substances that inhibit the growth of fungi and/or bacteria, antifoams, sequestering agents, emulsifiers, water-insoluble solvents, oxidising agents or air-releasing agents.
As preservatives there come into consideration formaldehyde-yielding agents, e.g. paraformaldehyde and trioxane, especially aqueous, for example 30 to 40% by weight formaldehyde solutions, imidazole compounds, e.g. 2-(4-thiazolyl)benzimidazole, thiazole compounds, e.g. 1,2-benzisothiazolin-3-one or 2-n-octyl-isothiazolin-3-one, iodine compounds, nitriles, phenols, haloalkylthio compounds and pyridine derivatives, especially 1,2-benzisothiazolin-3-one or 2-n-octyl-isothiazolin-3-one.
There come into consideration as sequestering agents, for example, nitrilotriacetic acid sodium salt, ethylenediaminetetraacetic acid sodium salt, especially sodium polymetaphosphate, more especially sodium hexametaphosphate; as emulsifiers especially adducts of an alkylene oxide and a fatty alcohol, more especially an adduct of oleyl alcohol and ethylene oxide; as water-insoluble solvents high-boiling, saturated hydrocarbons, especially paraffins having a boiling range of approximately from 160 to 210xc2x0 C. (so-called white spirits); as oxidising agents, for example, an aromatic nitro compound, especially an aromatic mono-or di-nitro-carboxylic acid or -sulfonic acid, which is optionally present in the form of an alkylene oxide adduct, especially a nitrobenzenesulfonic acid; and as air-releasing agents, for example, high-boiling solvents, especially oils of turpentine, higher alcohols, preferably C8- to C10-alcohols, terpene alcohols, and air-releasing agents based on mineral and/or silicone oils, especially commercial formulations consisting of approximately from 15 to 25% by weight of a mineral oil and silicone oil mixture and approximately from 75 to 85% by weight of a C8alcohol, such as 2-ethyl-n-hexanol. These are normally used in amounts of from 0.01 to 5% by weight, especially from 0.01 to 5% by weight, based on the total weight of the ink.
The inks preferably comprise N-methyl-2-pyrrolidone, diethylene glycol, glycerol or 1,2 propylene glycol, especially N-methyl-2-pyrrolidone, glycerol or 1,2-propylene glycol and more especially 1,2-propylene glycol, usually in an amount of from 2 to 30% by weight, preferably from 5 to 30% by weight and especially from 5 to 25% by weight, based on the total weight of the ink.
In a preferred embodiment, the inks used in accordance with the invention comprise urea or polyethylene glycol 200 in an amount of from 2 to 25% by weight, especially from 5 to 20% by weight.
The inks preferably also comprise solubilisers, e.g. xcex5-caprolactam in an amount of from 2 to 25% by weight, especially from 5 to 20% by weight, based on the total weight of the ink.
Preference is given to a process wherein the inks comprise
a) at least one acid dye of formulae (5), (8), (14), (18), (26), (27) and (28) and
b) 1,2-propylene glycol, N-methyl-2-pyrrolidone or glycerol.
Preference is given especially to a process wherein the inks comprise
a) at least one acid dye of formulae (5), (8), (14), (18), (26), (27) and (28),
b) 1,2-propylene glycol, N-methyl-2-pyrrolidone or glycerol and
c) at least one compound from the group E-caprolactam, urea and polyethylene glycol 200.
In a further preferred embodiment of the process according to the invention, the inks comprise
a) at least one acid dye of formulae (5), (8), (14), (18), (26), (27) and (28) and
b) xcex5-caprolactam.
The inks can be prepared in customary manner by mixing the individual constituents together in the desired amount of water.
The process according to the invention for printing fibrous textile materials can be carried out using ink-jet printers suitable for textile printing that are known per se.
In ink-jet printing, individual droplets of ink are sprayed onto a substrate in a controlled manner from a nozzle. For this purpose, predominantly the continuous inkjet method and the drop-on-demand method are used. In the continuous inkjet method, the droplets are produced continuously and any droplets not required for the printing are conveyed to a collecting vessel and recycled, whereas in the drop-on-demand method droplets are produced and printed as required; that is to say droplets are produced only when required for the printing. The production of the droplets can be effected, for example, by means of a piezo ink-jet head or by means of thermal energy (bubble jet). For the process according to the invention, printing by means of a piezo ink-jet head is preferred. Also preferred for the process according to the invention is printing in accordance with the continuous ink-jet method.
Fibrous textile materials that come into consideration are especially nitrogen-containing or hydroxyl-group-containing fibrous materials, e.g. fibrous textile materials of cellulose, silk or, especially, wool or synthetic polyamides.
The process according to the invention is used especially preferably to print silk or silkcontaining mixed fibrous material. As silk there come into consideration not only natural silk and cultured silk (mulberry silk, Bombyx mori) but also the various wild silks, especially tussah silk, and also eria and fagar silks, slub silk, Senegal silk, muga silk, and also mussel silk and spider silk. Silk-containing fibrous materials are especially blends of silk with polyester fibres, acrylic fibres, cellulose fibres, polyamide fibres or with wool. The said textile material can be in a wide variety of processing forms, e.g. in the form of fibres, yarn, or woven or knitted fabrics.
For printing silk or silk-containing fibrous material, the fibrous material is preferably subjected to a pretreatment. To that end the fibrous material is pretreated with an aqueous liquor comprising a thickener and, where appropriate, a hydrotropic agent. The thickeners preferably employed are alginate thickeners, such as commercially available sodium alginate thickeners, which are used, for example, in an amount of from 50 to 200 g/l of liquor, preferably from 100 to 200 g/l of liquor. The hydrotropic agent preferably employed is urea, which is used, for example, in an amount of from 25 to 200 g/l of liquor, preferably from 25 to 75 g/l of liquor. The liquor may in addition comprise further ingredients, e.g. ammonium tartrate. The liquor is preferably applied to the fibrous material according to the pad-dyeing method, especially with a liquor pick-up of from 70 to 100%. Preferably, the fibrous material is dried after the above pretreatment.
It is also possible in accordance with the process of the invention to use natural or synthetic fibrous polyamide materials. There comes into consideration as natural fibrous polyamide material especially wool. There come into consideration as synthetic fibrous polyamide material, for example, fibrous polyamide-6 and polyamide-66 materials.
After printing, the fibrous material is dried if necessary, preferably at temperatures of up to 150xc2x0 C., especially from 80 to 120xc2x0 C., and then subjected to a heat-treatment procedure in order to complete the printing, that is to say to fix the dye.
The heat treatment can be effected, for example, using a hot batch process, a thermosol process or, preferably, a steaming process.
In the steaming process, the printed fibrous material is subjected, for example, to treatment in a steamer with steam which is optionally superheated, e.g. at a temperature of from 95 to 180xc2x0 C., advantageously at from 95 to 130xc2x0 C., especially using saturated steam.
The printed fibrous material is then usually washed off with water in customary manner.
Both the ink-jet printing and the subsequent drying and fixing can also be carried out in a single step, which means, especially, that those steps are carried out continuously, that is to say, apparatuses for the inkjet printing, the drying and the fixing are mounted one after another and the fibrous material to be printed is moved through them continuously. The apparatuses for the ink-jet printing, the drying and the fixing can also be combined in a single machine. The fibrous material is transported continuously through the machine and is thus in the finished state when it leaves the machine. The drying can be effected, for example, by means of thermal energy (as indicated above for example) or especially by means of infrared radiation (IR). The fixing can be effected, for example, by means of ultraviolet radiation (UV) or by means of thermal energy (as indicated above for example). It will be understood that the ink-jet printing can also be carried out separately and the drying and fixing performed continuously as indicated above, e.g. in a single machine.
Using the printing processes indicated above it is possible to print fibrous materials either in a single shade or in a variety of shades. When the printing is in one shade, the fibrous material can be printed over the entire surface or with a pattern. The use of a single ink is, of course, sufficient for that purpose, but the desired shade can also be created by printing with a plurality of inks of different shades. When the fibrous material is to receive a print having a plurality of different shades, the fibrous material can either be printed with a plurality of inks that each have the desired shade or printed in such a manner that the shade in question is created (for example by printing the fibrous material with inks of different shades one on top of another, thus producing the required shade).
It is also possible to print a sheet-form fibrous material on both sides. In that case, for example, one side of the fibrous material can be printed in one shade, e.g. over the entire surface, and the other side of the fibrous material is printed with a pattern in one or more different shades. It will be understood that, in principle, that other side can likewise be printed in one shade over its entire surface. Such a process can be carried out, for example, by having one or more print heads arranged on each side of the sheet-form fibrous material to be printed. Both sides of the fibrous material are thus printed simultaneously. The print heads on each side of the fibrous material can be arranged either directly opposite one another or laterally displaced with respect to one another. The fibrous material is usually moved along between the print heads. Using this embodiment it is possible to achieve interesting effects, which are visible especially when the sheet-form fibrous material is folded over.
A further interesting embodiment relates to so-called xe2x80x9cimagingxe2x80x9d, in which an original, that is to say an image that is to be reproduced by the print, is digitised, for example by means of a video camera or a scanner. The digitised image is transferred to a computer, which then prints the image onto the fibrous material by means of an inkjet printer. Of course, the digitised image may already be stored in the computer, so that digitisation is unnecessary. For example, an image to be printed may already have been created on the computer using graphics software. The image to be printed may also be, for example, letters, numbers, words, all kinds of patterns and also complex multi-coloured images. Multi-coloured images can be created, for example, by using a plurality of inks of different shades.
The prints obtainable by the process according to the invention exhibit good all-round properties; for example they exhibit good fastness to light, good wet-fastness properties, such as fastness to water, to washing, to seawater, to crossdyeing and to perspiration, good fastness to chlorine, fastness to rubbing, fastness to hot pressing and fastness to pleating, as well as sharp outlines and high colour strength. The printing inks used are distinguished by good stability and by good viscosity characteristics.